1. Field of the Invention
The present invention relates generally to electric power control and more specifically to self-protected, intelligent power control module. The present invention, in specific embodiments, can be used as a power control center for a vehicle such as a motorcycle, automobile, boat or airplane and many industrial and defense applications where protection of a load is essential.
2. Description of the Prior Art
For years, electromechanical relays have been used in a wide variety of power control and other electrical applications. These mechanical devices, which are built of a coil and contacts, have demonstrated considerable reliability; however, they suffer from numerous problems associated with having moving parts. In particular, mechanical relays are subject to arching and sparking. In applications where it is required to switch a high DC voltage, the cost of a mechanical relay grows very rapidly. The switching of the coil leads to destructive voltage spikes (a fly-back voltage), while considerable power is needed to activate the coil (sometimes ten watts or more). In addition, material fatigue can shorten the life of a mechanical relay, and reliability can suffer from shock and vibration. An average electromagnetic relay is normally related for around 900,000 cycles. A solid state relay, on the other hand, can perform 5,000,000 cycles in several hours. These types of mechanical issues can be of major concern when the relay is used in harsh environments. For example, many vehicles, such as cars, tractor/trailers, heavy vehicles and aircraft typically use numerous relays in their various systems. Many such relays are also exposed to environmental corrosive substances (liquids, gases and the like). These substances can cause mechanical corrosion that can lead to breakdown. Another severe problem with mechanical devices like relays is that they have only and abrupt on or off transition. This introduces additional large transitional spikes. Solid state devices, on the other hand, can be designed to make timed off and on transitions.
Modern solid state power devices can be built with internal protection using field effect transistors with integrated current and temperature sensing. This allows building self-protective power devices with low voltage field effect transistors. In the past, a low value series resistor was inserted in series with the load (or bypassing a portion of load current) to allow current measurement. However, the extra heat generated by the resistor can create a problem. In addition, the addition of the resistor increases the overall resistance of the channel thereby lowering efficiency. It would be advantageous to eliminate this resistor.
In many power applications, a fuse is a common safety device that protects the power source and the connective conductors in the case of a problem with the load. If the load suddenly starts to consume excessive power, it is well known in the art that the fuse is designed to burn out and break the circuit thus removing voltage from the load and preventing further current flow preventing further damage and any fire hazard. Quite often, it is not an easy task to select the proper fuse. Many times, initial (turn-on) transient current draw from a load is much higher than normal operation load current. This can be countered by either using a fuse with a much higher than needed rating or by using a device known as a slow-blow fuse. A slow-blow fuse times before blowing. These fuses generally cost more than regular fuses. The fuse itself, has no built-in protection and will generally be damaged from a spike or current draw higher than it's rating that lasts too long. It would be advantageous to have a power control module that presents a combination of a protective device with characteristics of a slow-blow fuse with the additional feature of turn-off when current exceeds a particular value for a particular time. This power control module could withstand higher surge currents and avoid damage by excessive current. This power control module should also minimize false disconnection.
An Inherent problem with a fuse is an un-restorable power disconnection due to an overload. A burned fuse must be replaced, and that takes a time and human involvement. The result is lost production time and/or increase costs. In some cases, when a spare fuse is not available, the replacement made from any available and untested conductor. This dangerous practice can result in substantial danger and/or damage. Some of the newer semiconductors and electronic fuses have somewhat improved reliability by temporarily disconnecting of current flow during overload. However, some of them only withstand several trips, and none of them inform of a problem with a load.